Cards have been proposed wherein a substance which undergoes a change due to temperature, humidity, radiation dose or the like is partially painted on or affixed to a card substrate and performs the function of a sensor. For example, a card is known wherein the surface of the card is printed upon with a liquid crystal capsule ink the color of which changes with a change in temperature.
Cards of this type are simple in structure and easy to manufacture but the results of detection can be ascertained only by a change in color or the like and cannot be read directly from the card as an electric signal. In addition, transitory values obtained during detection can only be ascertained qualitatively, there is no way that the results of detection can be accumulated quantitatively, and a change with the passage of time cannot be stored. Consequently, these sensor cards can only be used in very limited applications.
The specification of Japanese Patent Application Laid-Open (KOKAI) No. 62-289727 discloses a sensor card comprising a sensor for sensing an environmental condition such as temperature and outputting an electric signal indicative of the condition sensed, a microprocessor, to which the electric signal from the sensor is applied as an input, for determining whether the value indicated by the signal lies within predetermined allowable limits, and display means for displaying the results of the determination made by the microprocessor.
However, when a value sensed by the sensor falls outside the allowable limits, this proposed sensor card merely causes the display means, which can be any suitable means such as a liquid crystal display device, to present a display to the effect that an abnormal state has occurred. The card is incapable of accumulating the results of measurement, and such results cannot be read out of the card to an external device. Accordingly, the display means must be monitored constantly and it is not possible to keep track of a change in an environmental condition with the passage of time.
Further, the specification of Japanese Patent Application Laid-Open (KOKAI) No. 61-58793 discloses an IC medical examination card comprising a temperature sensor for sensing body temperature, a display section for displaying body temperature sensed by the temperature sensor, and a memory for storing the body temperature sensed by the temperature sensor The card is so adapted that body temperature data stored in the memory can be read out to an appropriate terminal.
However, this IC medical examination card is utilized for very special purposes, namely the monitoring of a patient's body temperature and the supervision of medication. In actuality, measurement of body temperature is performed in response to pressing of a switch by the patient himself, meaning that the card is not adapted to enable measurement of temperature at desired time intervals. Consequently, human intervention is a requisite, general external physical phenomena cannot be measured automatically and continuously, and it is not possible to keep track of a change in these physical phenomena with time.
The specification of Japanese Patent Application Laid-Open (KOKAI) No. 62-265525 discloses an environmental sensing card comprising a sensor for outputting an electric signal commensurate with a change in the environment, decision means which, upon receiving the electric signal from the sensor, determines whether the measured value lies within allowable limits, a timer for measuring time, memory means for storing the results of the determination made by the decision means, measurement data and the prevailing time, and display means for displaying the results of determination, the measurement data and the time. In this environmental sensing card, however, the results of determination, the measurement data and the like are merely displayed by the display means disposed on the card and cannot be output to an external device. As a result, this card does not readily lend itself to tracing of a change in measurement data with the passage of time.